A known data recorder detects a specific behavior of a vehicle and records a control data of the vehicle at a time of detecting the specific behavior in a data-writable non-volatile memory. In this data recorder, the specific behavior is a behavior that can occur in conjunction with a driver's operation of the vehicle (see Patent Document 1). According to this kind of data recorder, analysis of the control data stored in the non-volatile memory enables a detailed investigation of a cause of occurrence of the specific behavior.
In the data recorder, when it is determined that a detection condition for a preset behavior is satisfied, the data recorder determines that the preset behavior has occurred. Patent Document 1 proposes that the detection condition be dynamically set (i.e., changed) in accordance with a vehicle traveling environment, an operator (driver) identification information, or an operator history information such as a driving skill, accident history and the like.
By the way, an electronic control unit for controlling a vehicle engine or the like is equipped with a failure detection function called also a diagnostic function. The failure detection function diagnoses a variety of failures based on information from in-vehicle equipment such as a sensor and the like in order to determine whether or not a failure has occurred. When determining that a failure has occurred, the failure detection function records a failure information (also called “Diagnostic Trouble Code” (DTC)) indicating the occurrence of the failure in a data-writable non-volatile memory. For this kind of electronic control unit, see Patent Document 2.    Patent Document 1: JP2000-185676A1 corresponding to U.S. Pat. No. 7,079,927B2    Patent Document 2: JP 2009-59334A1 corresponding to US 2009/0037044A1
In relation to the above, the inventor of the present application has found out the following. When a technique of changing the detection condition for a specific behavior of Patent Document 1 is applied to the data recorder, unneeded detection of a specific behavior can be reduced, and consequently, a storage resource for storing control data can be saved.
However, regardless of whether the technique is applied or not applied, upon detecting a specific behavior, a conventional data recorder records a control data of the vehicle without taking into account a cause of occurrence of the detected behavior. Therefore, even in cases where a detected specific behavior is a behavior occurring in conjunction with a failure of the vehicle, the control data is recorded. The storage resource is uselessly consumed.
For example, a “sudden increase in engine revolution” may be set as a specific behavior to be detected. In this case, even if the engine revolution suddenly increases due to a vehicle throttle failure, the data recorder detects the sudden increase in engine revolution and records the control data at the time of detection in the non-volatile memory. Additionally, the above-described failure detection function of the electronic control unit of the vehicle also records the failure information indicating the throttle failure. From the stored failure information, it is possible to recognize that the throttle failure is a cause of the sudden increase in engine revolution. Therefore, the cause of the sudden increase in engine revolution can be identified without the investigation of the control data recorded by the data recorder. The control data is a useless data in this case.
As can been seen, the data recorder records a practically-useless control data, which is a control data recorded at a time of the detection of a specific behavior whose cause can be identified from the failure information reordered by the failure detection function. This results in large consumption of the storage resource for control data. Therefore, it is difficult to secure a storage area for a control data that is really to be recorded.